During assembly of packaged semiconductor ICs, the bottom side of a semiconductor IC die is typically attached by a solid form dielectric die attach film (DAF), such as a fully cured epoxy, to a die paddle (or die pad) of a leadframe. Bond pads on the IC die are then attached to metal terminals of the leadframe by bond wires.
Some ICs are designed to electrically contact the bottom side of IC die, while other ICs are designed for the bottom side of IC die to be electrically isolated from the die pad. For packaged ICs where the IC die needs its bottom side to be electrically isolated from the die pad, and a potential difference exists between the bottom side of the IC die and the die pad during operation, electrical leakage between the bottom side of the IC die to the die pad through the dielectric DAF due to DAF isolation failure can lead to yield loss during electrical test, or lead to electrical failures during field use.